1. Field of the Invention
The present invention relates to a resist composition suitable for the formation of fine, high-resolution resist patterns, a resist pattern forming process using the resist composition, and a method for manufacturing a semiconductor device using the resist composition.
2. Description of the Related Art
Currently, the scale of integration of semiconductor integrated circuits has been increasing to a level that enables practical use of LSIs and VLSIs, with the linewidth of interconnection patterns reduced to as small as 0.2 μm or less and with a minimum linewidth of 0.1 μm or less achieved. The lithography technology is extremely important in the formation of finer interconnection patterns; the lithography technology comprises the steps of coating a workpiece substrate with a resist film, selectively exposing the resist film followed by development to form a resist pattern, dry-etching the substrate while using the resist pattern as a mask, and removing the resist pattern to obtain desired patterns (e.g., interconnection patterns). Attempts have now been made in this lithography technology to achieve formation of much finer patterns by reducing the wavelength of exposure light (i.e., light used for exposure) and further by using electron beams and/or X-rays.
Chemically amplified resists containing photoacid generators hold promise as resist materials that are applicable to lithography using electron beams, X-rays, etc. Irradiating the chemically amplified resist for instance with an electron beam, X-ray, or focused ion beam causes generation of acid from the photoacid generator, and subsequent baking process causes catalyzed reactions by which portions of the resist irradiated with the electron beam are made alkali soluble (for positive-type resists) or alkali insoluble (for negative-type resists). Thus the chemically amplified resists can be made highly sensitive to actinic radiation by increasing apparent quantum efficiency. These chemically amplified resists generally comprise a base resin, a photoacid generator, various additives, an organic solvent, and the like. Among them, negative-type chemically amplified resists comprise a crosslinking agent in addition to these ingredients.
In the lithography process using an electronic beam, electrons entering the resist film carry electric charge and thus they interact with the atomic nuclei and electrons of substances present in the resist composition upon application of the electron beam. For this reason, when an electron beam is incident on a positive-type resist film 210 formed on a substrate as shown in FIG. 26A and on a negative-type resist film 220 formed on a substrate 200 as shown in FIG. 26B, beam scattering (forward scattering) occurs, and thereby the beam-irradiated area of each of the resist films 210 and 220 becomes larger at bottom than at surface. As a result, the cross section of the resist space pattern of the positive-type resist (i.e., an opening 214 between adjacent lines of a resist pattern 212), obtained after development, has a reverse tapered shape as shown in FIG. 26C, whereas the cross section of the resist space pattern of the negative-type resist (i.e., an opening 224 between adjacent lines of a resist pattern 222), obtained after development has a forward tapered shape as shown in FIG. 26D.
The formation of such abnormal resist pattern shapes, especially reverse tapered shapes, prevents accurate measurement of pattern dimensions (as viewed from the top), making it difficult to achieve fine patterning upon manufacture of semiconductor devices.
The abnormal pattern shapes involved in the lithography using an electron beam is a reflection of electron beam scattering profile; the greater the resolution of the resist the greater the reproducibility of the electron beam scattering profile on the resist, and hence the pattern shapes become worse to a greater extent. To overcome this problem the following method has been adopted in the art: The resolution of the resist film is reduced by adjusting the alkali solubility of the resist material, allowing the resist film to gradually dissolve from outer surface toward substrate to form a resist pattern with a small taper angle, or a substantially vertical resist pattern. This method, however, has met with difficulty in forming finer patterns because the pattern size obtained after development is significantly large compared to the electron beam-irradiated area.
For example, Japanese Patent Application Laid-Open No. 2005-91415 discloses a method of forming a resist pattern with a space pattern whose cross section has a forward tapered shape, wherein the resist pattern is produced by using a positive-type resist material whose glass transition temperature increases by irradiation with an electron beam, and the surface of the resist pattern is irradiated with an electron beam to increase the glass transition temperature of the upper layer of the resist pattern followed by baking to fluidize the non-irradiated lower layer of the resist pattern to allow the lower opening to shrink. This method, however, is directed to first form a resist pattern with openings whose cross sectional shapes are rectangular and then make them forward tapered, rather than forming a resist pattern with openings whose cross sectional shapes are forward tapered by preventing them being reversed tapered. In addition, this method is inefficient due to the fact that various processes follow the formation of resist pattern.
Moreover, JP-A No. 2005-208365 discloses a positive-type resist composition capable of formation of shapes with an excellent pattern profile, which is achieved by the addition of acid-decomposable resin having a specific structure, and discloses the fact that it is preferable for this positive-type resist composition to further contain a basic compound in order to minimize change in its ability from exposure to heating. This positive-type resist composition, however, merely incorporates therein a single basic compound and thus is insufficient for high-precision control of the taper angles of openings of a resultant resist pattern.
Thus, the current situation is that there has not been provided any resist composition and related technologies, which are capable of prevention of the formation of abnormal resist pattern shapes for efficient, high-precision formation of fine, high-resolution resist patterns.